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Norman Sperling
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Norm Sperling’s Great Science Trek: 2014

San Luis Obispo
Santa Barbara
Palm Springs
Death Valley
El Paso
Corpus Christi
Baton Rouge
Key West
Winter Star Party, Scout Key

MARCH 2014:
up the Eastern seaboard

APRIL 2014:
near I-40, I-30, and I-20 westbound

MAY 2014:
near US-101 northbound
May 17-18: Maker Faire, San Mateo
May 23-26: BayCon, Santa Clara

California till midJune

JUNE 2014:
Pacific Northwest

JULY 2014:
Western Canada, eastbound

AUGUST 2014:
near the US/Can border, westbound
August 22-on: UC Berkeley

Speaking engagements welcome!
2014 and 2015 itineraries will probably cross several times.


Your Textbook

© 2002 Norman Sperling. Excerpted from What Your Astronomy Textbook Won't Tell You, 0-913399-04-3.

Whichever textbook you use, you need to understand its context.

Your textbook contains a lot of features to help you learn the concepts and information. Use the captions, the glossary, the learning objectives, the chapter-end questions, and the further readings, every time they'll help you learn, not only when your prof assigns them.

Your textbook is far more up-to-date, much better illustrated, and far more informative than

my introductory-astronomy textbook:

George Abell: Exploration of the Universe, 1964

I used George Abell's Exploration of the Universe in 1965 as a freshman at Michigan State. It was exciting! Not only did it shovel nifty information at me, it conveyed the excitement of research, and the latest perspectives. It even included a few color pictures. (Textbooks didn't get color on every page till the late 1980s. Prices skyrocketed because that's a lot more expensive to prepare and print.)

When I look at Abell's textbook now, however, I cannot help but chuckle. It is so naïve, so ignorant! The pictures look crude, because we have much better technology nowadays. The data are elementary. Spacecraft had only just reached Mars and Venus. Some concepts seem rather strange because we think of those things differently now. There is no mention of background radiation (discovered later that year) or pulsars (they weren't discovered till 1968), and no spacecraft pictures of Jupiter. Computers were huge, clunky, and rare. In so many ways, they didn't understand their clues – they didn't know impact craters pepper the whole solar system, and they didn't know rings circle all the big planets.

But my text was certainly a good-faith rendition of the astronomy of its era. The fact that it gave me no hint of all that was to come reveals a trait common to most textbooks: they are overly-positive. They concentrate so much on what they DO know that they neglect to point out what they DON'T know.

Abell's book was definitely a big improvement over the previous dominant textbook:

Robert H. Baker: Astronomy, 1930

Baker's book went through 10 editions from 1930 clear into the 1970s, a huge span for any textbook. I often checked it out of my city library while in high school, and was surprised it was not the one my prof required in college … surprised, and soon happy. That's because Abell deliberately included astronomy's excitement, and Baker never did. All the data and pictures and understandings of its time are there – the pictures were the very best available – but recited in a dry, declaratory way. That's the kind of person Baker was. Charles J. Peterson relays this story witnessed by a former student of Baker's:
One day a student approached Baker in his office at the University of Illinois to seek help on a concept which he was having difficulty understanding. Baker reached over to his bookshelf for the latest edition of his text. He thumbed to the relevant page and proceeded to read the paragraph pertaining to the student's inquiry.
"I don't understand," responded the student.
Baker read the paragraph a second time.
"That's what I don't understand," replied the student.
Baker then read the paragraph for a third time.
"But I still don't understand," lamented the poor student.
Baker returned the volume to the bookshelf and turned to face the student. "I'm sorry, but I can't help you," he said. "I've given it the best shot I can."

Baker's book is a good-faith rendition of the astronomy of its era, but laughable now. It is so naïve, so ignorant! How primitive they were! They didn't know that galaxies were a big story. Spacecraft were still science fiction. Computers were undreamt of. And so on. Astronomers back then were just as smart and clever as modern ones, but they had a lot less to go on, and it shows.

Nevertheless, Baker's book marked a major improvement over:

Forest Ray Moulton: Astronomy, 1906

Moulton was a leading astronomer of his time, teaming with Thomas C. Chamberlain to propose how the solar system might have formed as a result of another star coming very close to the Sun. Though later data disproved the Chamberlain-Moulton theory, it was advanced for its era.

Moulton's book is now a giggle-factory. The writing is not just passive-dull but downright stodgy. The contents are so naïve, so ignorant! This was before radio astronomy, before anyone knew how fusion works. It's not that much is wrong, but it sure makes you appreciate how much has been learned since then.

Yet it, too, was a good-faith rendition of the astronomy of its era: full of the latest data, and a few recent pictures. And Moulton marched in the forefront of education: his book was also chopped into small sections and marketed for correspondence courses, an early form of "distance learning". Moulton's textbook first appeared in 1906, and remained in print through the edition of 1938.

For all its shortcomings, Moulton's text was a major improvement over the previous dominant text:

Charles A. Young: A Textbook of General Astronomy for Colleges and Scientific Schools, 1888

Young was a veritable textbook factory. He produced several different levels of text, topped by this full-math version for the most technical students, and cut down successively for non-math college students, high-school students, and, in Lessons in Astronomy, for junior-high. I've often thought that should have been titled "Lessens" because of how much Young lessened the book. General Astronomy went through about 7 editions from 1888 to 1916.

This book tells you what astronomy knew at the time. It is so naïve, so ignorant! This was before most astrophotography, before mountaintop observatories, before anyone understood stellar spectra or how celestial objects evolve. Reading and laughing at an edition of this, which a student had picked up at a flea market, got me started in studying old textbooks. (Thank you, Carin!) Despite how poorly it has aged, it was a good-faith rendition of the astronomy of its age. And, in turn, a major improvement over:

J. Dorman Steele: A Fourteen Weeks Course in Astronomy, 1869

Steele was also a textbook-factory. He wrote A Fourteen Weeks Course in Chemistry, A Fourteen Weeks Course in Natural Philosophy, A Fourteen Weeks Course in Geology and others. They were illustrated with the latest woodcuts. And they told what astronomy understood back then. It is so naïve, so ignorant! And so awkward! They didn't yet have mountaintop observatories or much stellar spectroscopy. If you read Steele's book now, read it for humor or history, not for modern astronomy. Modern it is NOT! Steele published several editions from 1869 to 1884. But it was a good-faith rendition of the astronomy of its era. And, especially for readability, a huge improvement over:

Sir John Herschel: Outlines of Astronomy, 1830

For the 90 years from the time the author's father, William Herschel, discovered Uranus in 1781, till John Herschel died in 1871, they were dominant authorities. His is not merely a textbook but a compendium: it is intended to record full information about the entire subject. Practically every astronomer who could read English kept a copy of this book as the first place to check for information. Usually, they could find answers in Herschel. Only if this source failed did they seek another. And yet any student passing intro-astro now should be able to amplify many of the topics. Herschel's book isn't wrong, but it is very fragmentary.

The first edition was an instant hit in 1830, and new editions kept coming, and coming, and coming. John Herschel died 41 years later, but the book still stayed in print; the final edition came out in 1905. A 75-year press run! Staggering!

Though this book contains all the information you could want, it conveys absolutely no interest at all. Even the dullest lecturer is better than this! All the excitement had to come from the reader, because none can be found in the book itself. And, of course, the stilted language further highlights its age. It is so naïve, so ignorant, so turgid! This was before spectroscopy, before the physical nature of most celestial objects could even be described. Yet it was globally-proclaimed as a good-faith rendition of the astronomy of its era. And it was quite an improvement over:

John Bonnycastle: An Introduction of Astronomy in a Series of Letters from a Preceptor to his Pupil, 1786

This text is the earliest to which I've been able to trace the modern arrangement of topics. While things have certainly changed a lot in proportions and details, it seems to have been Bonnycastle whose arrangement was tweaked by succeeding authors to evolve into the common one used today.

This book is hard to read, not only because of its antiquated language, but also because of its antiquated typography: the "s" is a half-crossed "f", "ct" uses a flowery ligature, and so on. The bulk of this book deals with how things move, because almost nothing was known about what they are physically made of. This was before telescopes grew wider than 25 cm. This book is a good-faith rendition of the astronomy of its era. 8 editions of Bonnycastle's book were published in England between 1786 and 1822. It is so naïve, so ignorant! And so hilarious! Yet, in its time, it was a major improvement over:

James Ferguson: An Easy Introduction to Astronomy, for Young Gentlemen and Ladies: Describing The Figure, Motions, and Dimensions of the Earth; the different Seasons; Gravity and Light; the Solar System; the Transit of Venus, and its Use in Astronomy; the Moon's Motion and Phases; the Eclipses of the Sun and Moon; the Cause of the Ebbing and Flowing of the Sea, &c., 1768

James Ferguson had a full-size text (said to have interested William Herschel in astronomy) as well as this cut-down version.

This one takes the literary form of a dialog between college-man Neander and his sister Eudosia. Neander is home for term break, and his sister is pumping him for all the neat stuff he learned in his astronomy course. In the middle of page 75, Eudosia sighs.
Neander: Why do you sigh, Eudosia?
Eudosia: Because there is not an university for ladies as well as for gentlemen. Why, Neander, should our sex be kept in total ignorance of any science, which would make us as much better than we are, as it would make us wiser?
Neander: You are far from being singular in this respect. I have the pleasure of being acquainted with many ladies who think as you do. But if fathers would do justice to their daughters, brothers to their sisters, and husbands to their wives, there would be no occasion for an university for the ladies; because, if those could not instruct these themselves, they might find others who could. And the consequence would be, that the ladies would have a rational way of spending their time at home, and would have no taste for the too common and expensive ways of murdering it, by going abroad to card-tables, balls, and plays: and then, how much better wives, mothers, and mistresses they would be, is obvious to the common sense of mankind. – The misfortune is, there are but few men who know these things: and where that is the case, they think the ladies have no business with them; and very absurdly imagine, because they know nothing of science themselves, that it is beyond the reach of women's capacities.
Eudosia: But is there no danger of our sex's become too vain and proud, if they understood these things as well as you do?
Neander: I am surprised to hear you talk so oddly. – Have you forgot what you told me two days ago? namely, that if you had been proud before, the knowledge of Astronomy, you believed, would make you humble?

Proto-feminism, 1768!

Neander's name means "new man". New, because he's going to college, even though he is from the newly risen moneyed commoners. Until his time, to attend either Oxford or Cambridge (the only colleges in England), one had to be a white, male, member of the Church of England, and member either of the nobility or the clergy. By that standard, I suppose that not one single one of my thousands of students would get into college! How about you? Well, they let us all in now. Let's make the best of it while we're here!

The Ferguson book now makes great comedy for its literary form, as well as for its phrasing and scientific contents. It is so naïve, so ignorant! And so hilarious! This was before Uranus was discovered, before gravity was proven to work beyond the solar system. The first edition was published in England in 1768, and the last in the US in 1819. Yet it was a good-faith rendition of the astronomy of its times, and a major improvement over:

William Whiston: Astronomical Lectures Read in the Publick Schools at Cambridge, 1715

Whiston was Isaac Newton's hand-picked successor as Lucasian professor at Cambridge. (Other famous Lucasian professors: early 2000s – Stephen Hawking; 2400s – Cmdr. Data.) Whiston had a varied career worth looking into. This book poses many difficulties for the modern reader: antiquated typography, stilted phrasing, passive dullness, and overwhelming concern with the today-minor issue of sky motions. Whiston published a Latin edition in 1707, his first English edition in 1715, and a second in 1727, the year Newton died. It is so naïve, so ignorant! And so hilarious! This was before achromatic telescopes, before the first predicted return of Halley's Comet. While the contents aren't wrong, they barely hint at the main thrusts of modern science. Yet Whiston's book was, in its turn, a good-faith rendition of the astronomy of its era, and a major improvement over its predecessors ...

Past, Present and Future

You get the point. Astronomy (if not its college textbooks) goes back to early printing, to mediaeval manuscripts, to ancient scrolls, to cuneiform clay tablets and hieroglyphic-engraved stone monuments. And because scientific knowledge progresses, each edition ages rather poorly, and after a while serves better as a poor example than a good one.

Your text stands at the front of this long line. It is the modern culmination of all these successive approximations to what astronomers had learned about the universe. It is a good-faith rendition of the astronomy of right now. It tells the best anyone knows. With spacecraft that have gone as far as ours, with telescopes as big as ours, this is what we have learned.

And it won't end with your book! The author is probably already updating it for the next edition. And future authors will publish new ones after that. Some of what it says may be wrong, but since we don't know which things, we teach as best we know. Many future discoveries will bring system to current odds-and-ends. Many future discoveries will bring up important aspects scarcely hinted at so far. But we can't teach them, because that stuff hasn't been learned yet.

20 years from now, we'll know a lot better than some of the things in your book. Will you be the author of that one? 50 years from now, a better text will outmode that one. And 100 years from now, a more-improved version will relegate that one to humor. And 1000 years from now, all those will look hopelessly naïve, ignorant, and mistaken! And hilarious!

We teach what we know and understand now because that's the best we can do. That's what your book tells, in all good faith, however incomplete or mistaken it may turn out to be. Study it well, use it for all it's worth, learn it as the best anyone can do so far, but learn it as a framework into which the improvements of the future can be plugged in.

[The same can be said for all subjects in which knowledge progresses. Learn all of those subjects with the same perspective.]


TEACHERS: Similar sets of new-to-old textbooks are now available for sale! In stock:
History of Science
Philosophy of Science

We can assemble similar sets in most academic subjects.
Contact normsperling [at] gmail.com to get yours. This is a VERY impressive lesson for students!

Unlearning, Degrees of Belief, and Feng Shui

Norman Sperling, BASIS, vol. 17, no. 6, March 1999, p3-4.

Most people know the detailed "ifs, ands, and buts" of their own specialties. To learn them often requires un-learning the simplifications of "common knowledge" and "conventional wisdom". Outside their specialties, however, most people don't know any better than to accept oversimplifications. So do most leaders, confronted by problems they are not expert in, and so do most mass media. And so do skeptics, though we often feel worse when we learn better.

The oversimplifications we learn abound with boundaries, but reality turns out to be much more muddled. This is true for countries, for languages, and for "mystical beliefs".

National Boundaries

Maps often portray national boundaries as a sharp change from one solid color to a contrasting one. That gives the false impression that the area all in one solid color is all one uniform place, changing abruptly at the boundary to a contrasting uniform place. Before the Soviet Union broke up, most Westerners considered "Russian" and "Soviet" to be synonyms, and many were surprised when the flow of events featured the national identities of Lithuania, Uzbekistan, Chechnya, and others.

I learned another dimension from Dr. A. Florsch, who gave me a grand tour of Strasbourg Observatory. As we gazed toward the nearby Rhine River, he told me "I am a Frenchman. My father was a German. His father was a Frenchman, and his father was a German. And we have never moved!"

Languages and Dialects

Language, too, is much more varied than generally appreciated. I was taught that "in Germany, they speak German". That gave me the false impressions that "Germany" is one uniform place and "German" is one uniform language. I later learned that there are not only different accents and regional preferences, but also local dialects which are unintelligible to speakers of the nationwide version. In Newsweek I read a linguist's comment that "a language is a dialect with an army." Most often, the dialect of the capital becomes the "national language", especially through radio and television.

The same certainly applies in China. My ex grew up speaking Yantai dialect. It's a version of Mandarin which is not intelligible to people who only know Beijing dialect. Cantonese, in 2 southern provinces where many Chinese in America originated, is also not intelligible to Beijing or Yantai or dozens of other Chinese dialects. Most Mainland Chinese can now understand Beijing Mandarin, though they continue to speak their local tongue.

Feng Shui

Before I married a Chinese woman, visited plain people in China (in contrast to just tourist sites), and talked so often with Chinese people in America, I would have bought the tone of some skeptics' rants against "feng shui" (pronounced "fung shway"). That is reported as the mystical belief that buildings and their furnishings must be arranged in certain ways for good luck, and certain other arrangements must be avoided to fend off bad luck. This gives the false impression that "feng shui" is a uniform belief, and that all Chinese swallow it whole. Reality is much more varied.

Yes, there are highly-respected people "proficient" in feng shui. And, yes, there are some users who "believe" their dictates. But the vast majority of practitioners and users operate much more casually. Hardly anyone concentrates on feng shui. For most, it is little more than "that chair will look good over there".

It's hardly different from the interior design practice of one of our neighbors. When she says "that chair will look good over there", clients take her advice. They don't call her mystical, but they can't explain her skill, either.

It is the varying degrees that most media, politicians, and skeptics miss. From my visits and conversations I have learned that China is a country with enormous variety in food, language, and scenery, and also enormous variety in beliefs, intensities of beliefs, and local leadership. I've learned that, since the central government relaxed its grip, when you hear "China cracked down on X", it really means that "One Chinese politician cracked down on X, but outside his influence, people generally went about their business as usual." And when you hear some skeptics say that "Chinese believe Y", interpret that as "Some Chinese believe Y, and many less so, and others not at all, and some contrariwise."

FFNs, LBBs, and LBMs

© Norman Sperling 2002. Excerpted from his book What Your Astronomy Textbook Won't Tell You, 0-913399-04-3.


When novices start to use their first telescope, they look at the sky's major showpieces, such as the Messier nebulae, clusters and galaxies. They're big and bright enough to show up in binoculars, and a beginner's telescope shows detail in many of them. In the background lurk many more faint objects.

Experienced skywatchers buy bigger and better telescopes, seeing ever-richer detail in more and more nebulae, clusters and galaxies. But always, in the background, there are even more objects, too small and faint to make out. Some irreverent amateur astronomers in San Jose call those background objects "Faint Fuzzy Nothings" – FFNs.

FFNs continue in the background as seen by big, professional telescopes, too. Look at a picture of a galaxy in your textbook. In the background you can often notice dim smudges. Each of those is a galaxy, too, but so much farther away that you can't make out as much detail. A 3-meter-wide telescope shows magnificent detail in objects that amateurs can barely glimpse – and in the background lurk uncountable thousands of more FFNs. A 6-meter telescope shows detail in those, and in the background, even more FFNs. A 10-meter telescope reveals detail in those objects ... and in the background, there are ever more FFNs. No telescope has ever been made that didn't find more FFNs in the background.


One day when I was visiting my brother, a bird-watcher, I noticed his log of sightings. Almost every entry included "LBB". He told me that LBB stands for "little brown bird". They are so common, so small, and so similar, that they're not worth examining to see which common species each one belongs to. They flock all over, they're usually there, and they're not the big or pretty or rare birds that bird-watchers prize.


The university's mycological society hosted a meeting about LBMs. Mycologists study fungi, and I didn't have to attend to figure out that "LBM" stands for "little brown mushroom". LBMs are so common, so small, and so similar, that they're not worth examining to see which common species each one belongs to. They're not the big or pretty or rare mushrooms that fungus-hunters prize.

There's more! In prospecting, ignore LGRs: "Little Grey Rocks". In wildflowers, ignore DYCs: "Darned Yellow Composite" flowers that fill meadows. Among stars, ignore MV red dwarves. Among meteorites, ignore L6 "ordinary" chondrites. Among galaxies, ignore dE dwarf ellipticals. In archaeology, ignore undecorated body shards (they don't have initials, but ignore them anyway). In entomology, ignore midges.

The same principle applies outside of science. In coin collecting, ignore small copper coins. In stamp collecting, ignore definitives. In antiquarian books, ignore textbooks. And in the serious study of literature, ignore science fiction.

This happens a lot in science. Beginners learn all the kinds of phenomena in the field, and quickly concentrate on certain ones, all but ignoring certain others. Sometimes practicality forces the distinction: some are available, others are too difficult to study. Often, though, it's about what's fashionable to study.

Technology advances at such a furious pace these days that it may be worth looking anew at common background items, using the latest devices. Most people don't pay attention to them. You just might recognize something interesting that no one noticed before.

The Dim, The Weak, and the Ugly

© 2002 Norm Sperling, excerpted from What Your Astronomy Textbook Won't Tell You

How does a researcher select what to research? How does an editor select what to publish?

In both processes, the humans involved are often attracted to bright and beautiful objects. For the researcher, "bright" means plenty of light is available, making it practical to take detailed photographs and spectra. For the picture-editor who has to select some items and leave out others, bright and beautiful objects beat dim and ugly ones.

This means that the results reported in textbooks, the press and research journals are not a fair sample.

Red Dwarf Stars

The most abundant type of star seems to be the red dwarf. It's certainly the most abundant type within 25 light years. The very closest star to the Sun, Proxima Centauri, is a red dwarf – but so dim that you need a telescope to see it. Even the brightest red dwarf is too dim to see without binoculars. Since red dwarves are very difficult to recognize, hardly any are known.

For all their abundance, they aren't studied by very many researchers. Compared to other types of stars, they're dimmer, so there is less light to study. They are generally thought to not do much, other than sporadic unpredictable flares, so there is little of interest to attract researchers.

If red dwarves were studied as intently as, say white dwarves or red giants, would more interesting things would be discovered about them?

Thin Nebulae

Bright, thick nebulae get lots of attention. For active nests of stars, for beautiful twists and knots, they look great. There are lots of thinner, dimmer nebulae cataloged, but only a few observers track them down. Mostly, thin, dim nebulae get ignored.

If thin nebulae were studied as much as thick ones, would more interesting things be discovered about them?

Dwarf Elliptical Galaxies

In nearby clusters of galaxies, the most abundant galaxy type is the dwarf elliptical. To see even the brightest requires a significant telescope. Beyond 50,000,000 light years, dwarf ellipticals are very difficult to recognize. Because they are small and faint, not many are known.

For all their abundance, they aren't studied by very many researchers. Compared to other types of galaxies, they're dimmer, so there is less light to study. They are generally thought to not do much, having little nebulosity and no big powerful stars, so there is little of interest to attract researchers.

If dwarf ellipticals were studied as intently as, say, spirals or giant ellipticals, would more interesting things would be discovered about them?

With Galaxies, as With People, Pictures Show the Most Attractive, Not the Most Typical

People who select illustrations for books, slide sets, and other media naturally tend to pick the most attractive examples. This leads to some important misunderstandings. People looking at the examples tend to think they're typical, when actually they are not.

"Spiral" galaxies, which physically are disc galaxies, are prettiest to most humans. Therefore, the prettiest spirals show up in books and slide sets a lot more than others do. Ragged and less-symmetrical spirals, and elliptical and irregular galaxies, hardly ever get selected, even though ellipticals are very abundant.

Most textbooks include a photo of the beautiful galaxy M 51, the "Whirlpool". This is the galaxy with the most obvious spiral appearance; smaller telescopes (perhaps 35 cm) will reveal its arms than any other galaxy's. Many books call M 51 "a typical spiral galaxy". It is actually one of the least typical! Very few disc galaxies have continuous arms that can be traced so far around. Hardly any other bright galaxy has such vivid arms. Enjoy the beautiful view, but don't swallow the claim that it is "typical". It isn't, which is why so many books include it. More typical galaxies don't look as handsome. Editors select the nicest-looking pictures, therefore making the selections anything but "typical".

Barred spirals, too, rarely look like their "typical" case, NGC 1300. That one, again, looks prettier and cleaner than most. That's a good reason to publish its picture, but it's wrong-headed to call it "typical".

Much the same applies to planetary nebulae, pre-stellar nebulae, and surface features on planets. Editors (and often researchers) select the brightest and most attractive ones. Dimmer and less-attractive examples may be more typical, but they're less-often studied and shown.

Contest! Open to all!
Identify the "blandest galaxy", "ugliest galaxy", "blandest nebula", "ugliest nebula", "blandest planetary surface feature", "ugliest planetary surface feature", etc. Winners may be published in later editions of this book, and on this website.

The Theory is Wrong But Handy

© 1999 Norm Sperling, originally published in Bay Area Skeptics Information Sheet, vol. 17, no. 7, May 1999, 2.

Soon after Nicholas Copernicus published his great book De Revolutionibus in 1543, he died. This prevented the Catholic Inquisition from punishing him for his heresy in moving Earth out of the center, and making it merely one planet among many orbiting the Sun.

Copernicus's Sun-centered system came somewhat closer than anything Ptolemaic to predicting planet positions in the sky. While Copernican predictions were noticeably closer, they were still not exact. We now know the big problem was the shape of the orbits: Copernicus clung to the ancient presumption that orbits must be "perfect" circles. They aren't, but nobody knew that in the 1500s.

Though the Roman Catholic Church emphatically denied Copernican theory - even placing it on its Index of Prohibited Works from 1616 to 1835 - they did permit using it as a handy-dandy computing technique for improved results; it simply must not be taught as "true". 'Go ahead and compute that way to get the best results, but don't believe the system.'

With 20/20 hindsight, some academics have snickered at this, because we know the Earth is not the center of everything. But carry the story a few chapters further:
* Tycho makes the sharpest positional measurements,
* Kepler determines from those that orbits are ellipses, and
* Newton derives Kepler's Laws from his own Law of Universal Gravitation.
* Centuries later, Einstein overthrows Newton, regarding gravity as warps in space-time.

To calculate the path of anything moving many percent of the speed of light requires Einstein's equations; that's how they found out that Newton was wrong. But almost everything that astronomy deals with moves less than 1% of the speed of light. At such slow speeds, the numbers from calculating Einstein's formula are identical with the numbers from calculating Newton's simpler formula. So, even now, practically everybody calculates with Newton's formula, and reserves Einstein's more complicated version for the rare cases where things move really fast. They know Newton is physically wrong, they just use it as a simpler way to compute and get the same result.

What these modern astronomers do is little different from what the Church advocated centuries ago: go ahead and use the handiest formula that gives the best result, but don't believe that it is physically true. To be fair, they should stop snickering at that old Church policy, or start snickering at themselves.

The Journal of Irreproducible Results
This Book Warps Space and Time
What Your Astronomy Textbook Won't Tell You

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